Maritime vessels require a coating on the submerged section of the vessel to prevent buildup of "sea growth", including algae, larvae, and spores from marine animals and plants. The accumulation of this type of growth on the vessel results in an increase in friction, i.e., greater surface area, between the hull and the surrounding water. Increased friction will be manifested by slower movement and increased energy consumption to propel the vessel through the water. Buildup of growth on a ship hull occurs most often when the ship is docked or moored, particularly in marinas or ports where water is not moving and thereby containing a higher concentration of marine organisms.
This buildup is obviously undesirable and the coatings normally employed by the industry to reduce or prevent marine life buildup up are called "antifouling paints". These paints contain inorganic and organic compounds that slowly leach out of the coating into the water surrounding the hull. The active components of the antifouling paints are typically heavy metal sulfides or oxides of nickel, manganese, iron, zinc, cadmium, cobalt, lead and mercury. Organic tins or pesticides are often included within the coating substrate. These heavy metals leach out of the ship coating forming a thin, highly concentrated laminar layer several microns thick surrounding the ship hull. The high percentage of the thousands of types of microorganisms that come in contact with this environment are killed by the complexation of these heavy metals with their proteins and enzymes. Any microorganism or animal that does succeed in attaching to the hull may eventually die after continued exposure to these purported toxins. Over time many of the heavy metals such as tin will hydrolyze and slough off with the top layers of the coating, taking with them any attached dead marine growth. This procedure results in a freshly exposed coating surface with more toxins able to leach from the surface. The antifouling coating must be reapplied new to the hull of a ship at the beginning of every boating season. The effective life of the coating is typically 9 to 12 months.
The problem confronting the industry is that the antifouling paints by the very nature of their efficacy contain materials that are considered to be toxic to the marine environment. Marine organisms and micro- organisms that have died as a result of the interference of these heavy metals with their metabolic pathways will be passed into the food chain in the marine environment.
This problem is most evident in small inlet waterways, lakes and streams where bottom samples and fish samples have shown increasingly high levels of these inorganic materials in recent years. Many of these waterways used for recreational boating activities also serve as reservoirs for potable water. Legislation has been proposed in many countries limiting or banning the use of antifouling paints in freshwater and sweetwater areas.
All maritime paints used as coatings for ship hulls contain these organic and inorganic substances as part of their antifouling mechanisms. Other types of technology have been introduced to reduce marine buildup on piers and oil platform pilings; these silicone rubbers and elastomers although reducing buildup have proved difficult to clean, which make them unusable as coating materials for boats. With the proposed restriction and potential banning on conventional antifouling paints, new technologies must be developed to fulfill the demanding requirements of this application. To date, no viable technologies have been introduced to the market as a potential replacement for inorganic and organic containing antifouling coatings.